Darn, looks like I missed most of the fun... I saw this paper last night, and wondered who even bothered to read that rag anymore, or if anyone would actually be duped by it. I got that answer quickly.
There's still enough left for me to take one big shot at it, however, so here it is.
Others have already commented on the editorial treachery and insufficient technique (welcome,
NutCracker!) that, alone, relegate this "work" to the comedy section. But there's even more.
Let's suppose, for sake of argument, we accept their argument, we accept their method, and we accept their data analysis -- we don't, of course, but just suppose -- and we agree with their conclusion that the upper block doesn't experience the "Big Jerk." What does this mean? The authors claim that it invalidates Bazant & Zhou's progressive collapse paper. But is this true?
We've discussed Bazant & Zhou any number of times here. The criticism generally concerns their
model of the collapse, rather than the calculations themselves. In their model, an admittedly simplified one, a simplified, rigid upper block is dropped the height of one story onto a simplified lower block, under the influence of gravity (and slightly opposed by the collapsing story -- a small correction is included for columns considered to be at their yield point at the start of the trial). This leads to a big bang, which as they calculate, cannot possibly be resisted by the columns on the next floor. Therefore, collapse progresses.
The authors observe that (again, playing along with their argumentation) there is no big bang. The opposing force supplied by the lower structure is a relatively continuous function (to the inadequate level of resolution present in their data, but again, play along). And this, they say, invalidates Bazant & Zhou's model, and thus their paper is wrong, collapse shouldn't have happened at all, 9/11 Was an Inside Jerb.
This is wrong. This is, in fact,
undifferentiated zebra puke.
Bazant & Zhou do not
require a "Big Jerk." Their model, as anyone who comprehends their paper knows, is about
energy and momentum. These are aggregate quantities -- energy is force times distance, i.e. the force is integrated over a period of motion. So if there's a "Big Jerk" or not, so long as the
total energy absorbtion of the lower structure is accounted for correctly, it will provide the right answer.
The authors of this paper, however, are looking at
instantaneous acceleration. They aren't dealing with a quantity that averages out. So they need much more precision, precision that isn't found in Bazant & Zhou's model. It isn't needed for that problem.
So, rather than show "Bazant & Zhou is wrong," they've shown "Bazant & Zhou is a poor model of instantaneous acceleration." Big deal. That's not what we're interested in. We're interested in the collapse.
One could also argue, with equal effectiveness, that the collision between the two blocks was not axial, and therefore Bazant & Zhou is wrong. The collisions are not axial, this is true; there is no reason at all to suspect the columns above just happened to land exactly on the columns below. But, again,
this doesn't matter. They model it this way because an axial impact is the
best possible case if you want the structure to survive.
What Bazant & Zhou present is an
upper bound. They put in all kinds of unlikely assumptions that favor collapse arrest. Axial impact is one of them. A square impact between upper and lower block is another. Mr. Szamboti and Dr. MacQueen are, really, taking issue with one of those assumptions, an assumption that we already knew from Day One was unrealistic.
So, what happens if we put in more realism?
We know the impact was not square. This is because the upper blocks
tilted first. The tilt smears out each and every impact.
Suppose each floor was 3.2 meters high. The structures were 64 meters across. So, if I tilt the structure by an angle of
θ = sin
-1(3.2 / 64) = 2.9 degrees, the bottom edge will be tilted over the height of an entire floor. At this amount of tilt or higher, at every instant, the upper block is in contact with the lower floors at the top, bottom, and everything in between. Were the upper blocks tilted by 2.9 degrees or more? You bet they were.
As a result, we don't expect a "Big Jerk" in the first place. At any given instant, the upper block is failing columns
gradually. There will be some that are just coming into contact, some that are reaching their buckling point, and some that have completely failed. There is no "Big Jerk" but a steady loading and failing of individual elements. As a result, there's no reason to suspect a sudden change in the structure's resistance. It is a fairly smooth phenomenon.
In fact, Mr. Szamboti and Dr. MacQueen's observation is evidence
in favor of a gravity-driven collapse. Think about it. They say there's no "Big Jerk." I agree with them. What this means is that the lower structure, in addition to being hit with an enormous force, was hit asymmetrically. Had there been a "Big Jerk," that would mean the structure, across its entire breadth, was resisting at once, rather than being hit piecemeal, one row of columns at a time. The square impact is
more likely to survive. The absence of the "Big Jerk" is only further evidence that Bazant & Zhou overestimated the structure's strength with their model, and therefore the collapse is even less in doubt than it was.
QED.
This is just another black eye for Dr. Jones and his ridiculous self-promotion. One would have to be deeply non-technical to even consider this argument plausible. This is evident from the follow-up questions being asked by the duped:
I'm not quite sure what you're rambling on about in your rant, but the primary question the paper is addressing is how did the rigid upper block separate itself entirely from the lower portion of the building and then crush everything below it, maintaining freefall speed?
Why didn't the other 90% of the building offer any resistance to slow the descent?
These questions are really not coherent. Regarding the first question, again,
only in the model does the upper block "separate itself entirely." What really happens is a lower floor failed, didn't fail at once, and this introduced a tilt. The remaining members on that particular floor couldn't hold the upper block, since tilting would shear any remaining connections, and the collapse begins. Bazant & Zhou are only estimating the initial energy, and their estimate is a fair one.
There are numerous other factors they didn't include that make collapse even more likely. The tilt is one of them. Another is that the next few floors to be hit were dramatically weakened due to impacts and fires. And if the second floor doesn't catch the collapse, there is no hope whatsoever for the third floor to catch it. The descending mass is speeding up over time, not slowing down.
Regarding the second question, the "other 90%"
does resist the collapse. That's why the collapse takes about 12 seconds instead of about 9 seconds. This resistance translates into absorption of 50% of the gravitational energy. That's a
lot of resistance.
If you're asking "why didn't the other 90% arrest the
initial collapse," it's very simple, and Dr. Bazant already answered this in his reply to Dr. Jones and cohorts, in a peer-reviewed (really peer-reviewed, not JONES peer-reviewed) letter. The reason is that the individual floors cannot transmit a force greater than their yield strength, no matter how hard they get hit.
Here's a strained analogy: Take a cinder block. Put an empty soda can on top of it. Now drop a bowling ball on the soda can. The cinder block will only see a small force while the can crumples -- no more force than the can will support. Once the bowling ball is done squashing the can and hits the cinder block, the block suddenly sees a much, much higher force.
This is true no matter how much you reinforce the base below the can. Similarly, the WTC Towers collapses really do hit only one floor at a time. Really. The individual floors push down at their yield strength, and that's it. That yield strength, as Bazant & Zhou demonstrate, is simply not enough at any time to stop the collapse. So the individual floor fails, the debris falls some more, picks up speed, and it all happens again. Except it happens more or less continuously. It isn't completely flat.
Now, I have a question of my own for
RedIbis:
Why do you allow yourself to be duped like this?
I understand you lack the technical insight. But consider the source. You know Dr. Jones's "journal" is no journal at all, but instead a
mouthpiece for his own club. You also know that his papers are a joke. They've put out over a hundred now, and with the exception of those from Dr. Greening,
GregoryUrich, and others trying to correct them, they're all garbage.
You know that Graeme MacQueen, in that very journal, tried to claim the FDNY must have been told WTC 7 could collapse, despite his own paper concluding that at least seven of them
must have
figured it out on their own. You also know that Mr. Szamboti (posting here as
realcddeal) pins his entire conspiracy theory on a baffling
rejection of reality, namely that the inward bowing seen and well documented by NIST is a lie, and only appeared at the instant of collapse, despite being shown the photographic evidence repeatedly. (I stopped responding to Mr. Szamboti shortly after
this episode, where in a performance worthy of McCarthy, he
accuses Gravy of being a "Dual Citizen," and y'all know what that means.)
So why? Why do you listen to these frauds, after all this time? How many times do they have to embarrass themselves for you to learn from it? 100 wasn't enough, will it take 1,000? Or is this the one that convinces you to stop buying their nonsense?
What will it take?
